210 MR. P. GROOM—CONTRIBUTIONS TO THE 
the roots passes into the rhizome. This would lead us to anti- 
cipate that there would be a relative increase in the number of 
the conducting elements of the xylem in the rhizome. And such 
is the case. This goodly development of xylem does not occur in 
the absorbing-rhizome of Corysanthes, for the reason given above, 
and probably also because stomata permit the excess of water to 
be given off. The xylem of the tuber of Epipogum nutans is 
well developed because the tuber stores water instead of giving 
it off through stomata. 
In subterranean parts of the saprophytes investigated there 
appears to be a very distinct mechanism to enable the plant to rid 
itself of any excess of water. In Lecanorchis, Aphyllorchis, and 
Corysanthes stomata occur on the subterranean axis and on the 
scales and are widely open (in alcohol specimens). In Lecanorchis 
there is, in addition, a hypodermal system of storage-tracheides in 
the scales. In Galeola javanica there are no stomata; but water 
can pass out through certain patches on the leaves when the 
epidermal walls are thin; under these patches there is an exten- 
sive hypodermal system of storage-tracheides. 
It is quite possible that in the holosaprophytes the stomata 
have another function, z. e. of assisting in the interchange of gases 
involved in respiration. 
Structure of the floral axis of Lecanorchis, Aphyllorchis, and 
Galeola.—The axis bears only a few and widely separate scales 
on its aerial part. Compared with the subterranean parts, the 
scales are fewer, smaller, and are not so long-lived. The axis is 
coated with an epidermis possessing thickly cuticularized outer 
walls; hence transpiration is slight. Many scapes of green 
orchids are very similar except for the thin green cortex, and are 
mainly conducting structures. So we shall not expect the struc- 
ture of these axes to be very dissimilar to that of a green scape: 
in fact we find that it is not so. The only difference lies in 
the greater number of stomata and the larger intercellular spaces 
in the green cortex (Spiranthes). In the holosaprophytes there 
is the typical general sclerenchyma-sheath, ordinary collateral 
bundles with protoxylem in the form of spiral or annular 
vessels. 
Epipogum nutans is as distinct in the structure of its floral 
axis as it is with regard to its rhizome. Its habitat—in marshy, 
moist, shaded regions—is reflected in its structure. Large 
intercellular spaces are in the ground-tissue and xylem. The 
conducting constituents of the xylem are narrow spiral or annular 
